ACI 544.7R-16 Report on Design and Construction of Fiber- Reinforced Precast Concrete Tunnel Segments

ACI 544.7R-16 Report on Design and Construction of Fiber- Reinforced Precast Concrete Tunnel Segments. 3.1—Fiber-reinforced concrete design codes, standards, and recommendations Fiber-reinforced concrete (FRC) precast tunnel segments have been designed using constitutive laws recommended by international design guides, codes, and standards such as German Concrete Association DBV (1992), RILEM TC 162-TDF, CNR DT 204/2006, EHE-08, fb Model Code 2010 (International Federation for Structural Concrete 2013), and ACI 544.8R. These documents propose stress- crack width or stress-strain constitutive laws of FRC as a linear post-cracking behavior (hardening or softening) or as a rigid perfectly plastic behavior based on bending test results. Alternatively, an approach using nonlinear fracture mechanics can be adapted to analyze cracking phenomena (Hillerborg et al. 1976). In ACI 544.8R, there are models that can be adopted to obtain required constitutive laws for the calculation of axial force/bending moment interaction diagrams for use with FRC precast tunnel segments. This document recommends the ACI 544.8R method that uses results of standard beam tests such as ASTM C1609/C1609M and BS EN 14651 to determine post-crack residual tensile strength as one of the key design parameters for FRC tunnel segments. 4.3—Load Case 3: Segment transportation Segments are generally transported to the jobsite as soon as specifed compressive and fexural strengths have been achieved in the stack yard. During transportation, the segments generally undergo various types of dynamic shock loading. As shown in Fig. 4.3(a), half of the segments for each ring are usually transported to tunnel-boring machine (TBM) trailing gear. Similar to the storage phase, wood blocks are used between the segments as stack support. The designer generally optimizes the distances between the wood blocks as well as the free edge of the segments to reduce the bending moments in the sections. An eccen- tricity of 4 in. (0.1 m) is usually recommended for eccen- tricity effects that may develop due to imperfect alignment of the stack supports. This load case also simulates the load condition that may be induced by forklifts at lift points that are spaced wider than the stack supports. Multiple segments can be picked up together by the forklift. A simply supported beam loaded with the appropriate forces, as shown in Fig. 4.3(b), may be used to represents this load case. In addition to a dead load factor of 1.4 as per ACI 318, a dynamic shock factor of 2.0 is also recommended to simulate the shock effects...